The present invention relates to a unique diamond/carbon/carbon composite useful as an integral dielectric heat sink, and a method for making such a composite. More particularly, the present invention relates to a diamond/carbon/carbon composite formed by depositing polycrystalline diamond on a carbon/carbon composite, and to an integral dielectric heat sink formed by depositing a metallic film on the diamond layer of the resulting diamond/carbon/carbon composite.
In recent years, demand has increased for high power, high density electronic devices used for advanced systems such as aircraft, spacecraft, and supercomputers. One known solution to this problem entails fabricating multichip module (MCM) circuitry with greater circuit density and more efficient electrical performance. However, while this process provides superior electrical performance, the increased circuit density raises the power density within the MCM, increasing the heat dissipation requirements. Ongoing improvements to heat sink materials must be made to avoid heat-induced failure of such electronic devices.
Semiconductor bases have been produced using composites comprising fibers, fiber bundles, and woven fiber bundles of graphite, boron, tungsten and glass. However, such composites do not have a very high thermal conductivity.
Carbon fiber reinforcements have made significant improvements in properties of composites of various polymeric, metal, and ceramic matrices. However, a limiting factor in the use of such fibers is their highly anisotropic thermal conductivity and their inability to match the coefficient of thermal expansion of the circuit material, which is typically silicon or gallium arsenide.
Various processes have been developed in recent years to produce synthetic diamonds for use as heat sinks in the electronics field. Although diamond is electrically insulating, diamond has the highest thermal conductivity found in nature. Thus, diamond is an ideal heat sink material for semiconductor devices. Diamond has other desirable properties including high hardness, high dielectric strength and breakdown fields, chemical stability, and a coefficient of thermal expansion (CTE) which is suitable for matching a wide range of CTE's of materials to which the composite is mated.
One process for synthesizing diamond is to use microwave assisted chemical vapor deposition to deposit diamond on silicon substrates. Such a process is described in Badzian et al, "Vapor Deposition Synthesis of Diamond Films", Proceedings of SPIE, Vol. 683, 1986. Another process involves growing diamond crystals by plasma chemical vapor deposition as described in Chang et al, "Diamond Crystal Growth by Plasma Chemical Vapor Deposition", J. Appl. Phys. 63(5), 1988.
Still other processes have been developed for production of layers of polycrystalline diamond on a substrate with recovery of flakes for use in composites. One such process is described in Banks, U.S. Pat. No. 4,437,962. A composite is produced by depositing carbon on a surface, creating diamond bonds in the carbon, removing flakes of the carbon, and mixing the flakes with a matrix material to form the composite material. However, the production of such flakes requires a relatively complex process.
Accordingly, there is still a need in the art for an improved composite having superior electrical and thermal performance, low density and high mechanical strength. Further, there is a need for an improved composite which may be used as a high thermal conductivity dielectric heat sink.